1. Field of Invention
This invention relates, in general, to hydraulic couplings, and specifically to hydraulic couplings used in undersea drilling and production applications. More particularly, the invention involves an integral metal to metal seal for a subsea hydraulic connector, the seal formed at the outer rim of the leading face of the male member of the coupling.
2. Description of the Related Art
Subsea hydraulic couplings are old in the art. The couplings generally consist of a male and a female member with sealed fluid passageways connecting therebetween. The female member generally is a cylindrical body with a relatively large diameter longitudinal bore at one end and a relatively small diameter longitudinal bore at the other. The small bore facilitates connection to hydraulic lines, while the large bore seals and slidingly engages the male member of the coupling. The male member includes a cylindrical portion at one end having an outer diameter approximately equal to the diameter of the large bore in the female member of the coupling. The male member also includes a connection at its other end to facilitate connection to hydraulic lines. When the cylindrical portion of the male member is inserted into the large bore of the female member, according to various embodiments of the device, fluid flow is established between the male and female members.
The male and female members of a hydraulic coupling each typically include a poppet valve slideably received within the bore of each member. Each poppet valve typically includes a conical valve face which seats, in the closed position, against a valve seat at one end of the bore. The poppet valve opens to allow fluid flow and closes the poppet valve face against the corresponding valve seat within the bore to arrest the flow. Generally the poppet valve is spring biased to the closed position.
The poppet valve also includes a poppet valve nose or stem extending from the apex of the valve face along the longitudinal axis of the poppet valve. Contact between the tips of the noses or stems of the male and female member poppet valves forces each valve face away from the valve seat of each member and into the open position for fluid flow therebetween.
Subsea couplings also generally include soft seals positioned within the female member bore to seal the junction between the male and female members. When the cylindrical portion of the male member is inserted into the large bore of the female member, the soft seals, resembling o-rings, either abut the end, or face, of the male member or engage the male member about its circumference. The hydraulic fluid is then free to flow through the male and female portions of the coupling, and the seals prevent that flow from escaping about the joint in the coupling.
The soft seals have numerous disadvantages, the principal ones being (1) the inability of the seal to withstand the deteriorating effects of the subsea environment for extended periods of time, and (2) the inability of the soft seal to contain the higher pressures being imposed on the hydraulic systems.
A crush-type metal seal is available which better withstands both the deteriorating effects of the environment and the higher pressures. The crush-type seal is positioned between the end of the male member of the coupling and the internal end of the large bore in the female member. When the male member is inserted into the female, the metal seal is crushed between the two members and a seal is effectuated between the two. Because of the crushing action, the seal can be used only once. If a coupling is separated for any reason, the once used crushed seal must be replaced with a new seal.
Various other types of metal seals have been placed either in a circumferential groove about the interior of the large bore in the female member, or at the interior end of that bore for engagement with the leading face or end of the male member. Typically, a metal seal is fully energized upon the establishment of fluid communication between the members. Hydraulic pressure urges the seal into engagement with one or both of the members, thereby fully energizing the seal. For example, the hydraulic pressure will urge the seal to expand radially against one or both of the coupling members.
Particularly in the case of face-type seals, there is no mechanism for retention of the seal in the female member. If the coupling is parted under pressure, the face-type seal will generally blow out of the female member receiving bore and be lost. There may also be risk of injury to the operator parting the coupling.
Many types of metal to metal seals also require preloading of the seal before fluid communication is established therebetween. In preloading the seal, the seal is partially energized, that is, the seal is urged into engagement with one or both members before it is fully energized. For example, some types of preloading force the seal to expand radially against one or both of the members before it is fully energized upon fluid communication between the members.
Some types of metal to metal seals require external preload devices for the seal. An external preload mechanism typically is used to prevent relative longitudinal movement between the male member and the female member. A problem with external preload devices is that such a device must overcome the fluid pressure which may urge the members apart. The external device must not only partially energize the seal, but also overcome the hydraulic pressure which urges the members to separate. This is a serious problem particularly when a high pressure is desired for hydraulic lines, and in such a case the hydraulic pressure may overcome the preload device and the sealing relationship may be lost.
The sealing relationship also may be lost in prior art couplings that do not employ external preload devices. This problem is caused by any relative longitudinal movement of the coupling members. Any longitudinal movement between the members cannot be tolerated without sacrificing the sealing relationship.